For me focusing an sct, the main cause for a bad focus curve with sgp is the occasional inclusion of extremely small features that aren’t stars and are unrealistically small. I have entered a feature request to measure the HFD in arc-seconds and reject stars smaller than a given minimum, in arc-seconds.
The second issue is that the HFD is not a consistent value for different stars in an image. I prefer to use fwhm for focus curves but I don’t have Pinpoint. Many people consider HFD to be more robust - but I don’t find that to be true. The inconsistency of HFD has an impact on the focus curve when the stars used for the calculation changes. This will result in an abrupt jump in the overall HFD driven mainly because different stars have different hfd values in a given image - and changing the stars used will therefor change the overall hfd.
If I take a focus curve with sct and I stay close to the focus and avoid donuts, then the focus works very well - with smart focus disabled - but only as long as the above two things don’t happen: a tiny small feature being counted as a star and pulling the curve down, or a sudden change in the stars used for the calculation - which can pull it up or down.
For me a focus run takes 2-3 minutes approximately due to 2x backlash unwinding and 2s exposures - 9 of them. But the time has little impact when focusing about every hour. Sharp focus is a priority.